Floatable base for marine drilling platform and method of operation



March 25. 1969 c. c. BROWN 3,434,293

FLOATABLE BASE FOR MARINE DRILLING PLATFORM AND METHOD OF OPERATION Sheet Filed May 8, 1967 A TTORNEVS March 25. 1969 c c. BRQWN 3,434,293

FLOATABLE BASE FOR MARINE DRILLING PLATFORM AND METHOD OF OPERATION Filed May 8, 1967 Sheet 5 of 5 A TTORNEJ 3,434,293 A'IFORM March 25. 1969 c. c. BROWN FLOATABLE BASE FOR MARINE DRILLING PL AND METHOD OF OPERATION Sheet Filed May a, 1967 6. BROWN AT'IURNEYS United States Patent 3,434,293 FLOATABLE BASE FOR MARINE DRILLING PLATFORM AND METHOD OF OPERATION Cicero C. Brown, Brown Oil Tools, Inc., P.0. Box 19236, Houston, Tex. 77024 Filed May 8, 1967, Ser. No. 636,820 Int. Cl. E02b 17/02; E02d 21/00 US. Cl. 61-465 8 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a base for a marine drilling platform and its method of operation, and more particularly to a type of base which is adapted to be floated in horizontal position on a water body to a drilling location and to be then up-ended and submerged to rest upon the underlying land.

Such base structures commonly-incorporate as the main support members, large diameter leg members which, when sealed, will function as buoyancy chambers to enable floating the structure and which, when suitably ballasted, can be up-ended to be sunk to rest in vertical position upon the underlying land. Moreover, such leg-type structures ordinarily are equipped with a plurality of drilling-through conduits enclosed within one or more of the legs to enable the drilling of a plurality of wells from the platform through the leg members.

In order to render such a base structure buoyant and floatable, the practice has been to seal-off the ends of the main leg members (and the enclosed drilling-through conduits by welding heavy steel plates across the ends of the leg members. When the structure has reached the drilling location and has been suitably ballasted to up-end and set it on bottom, the further practice has been to cut-off the enclosing plates at the upper ends of the legs and to then drill through each of the conduits in order to drill out the plate portion closing the lower ends thereof. This latter operation frequently encounters considerable difficulty, particularly when the base is set on a bottom composed of hard rocky materials, as is often the case. Drilling out the individual segments of the enclosing end plate against the resistance of the underlying hard rock formations has proven to be a matter of considerable difliculty, entailing substantial loss of time in preparing the base, with consequent large expense.

The magnitude of the problem and the attendant expense and time loss will be evident when it is considered that in one structure of the type described, each of the four main leg members is about 17 feet in diameter through which extend l2 drilling-through conduits, each about 38 inches in diameter. Thus, to clear these conduits requires the drilling-out of 48 heavy steel plate portions approximately 36 inches in diameter, which becomes an exceptionally difiicult task when the end plates are backed directly by hard rock on which the structure is landed.

The present invention is directed to a platform-supporting base of the general character described, but in which each of the individual drilling-through conduits is provided with a removable plugging device, particularly for plugging the ends thereof, which will be disposed adjacent the underlying land when the structure is in place. These plugging devices are constructed to seal each of the conduits against entrance of water to enable renderin g them buoyant and are arranged to be easily removable by means of a suitable pulling tool, such as a conventional overshot or spear, to clear the conduits for subsequent well drilling operations, and thereby obviating the need for drilling out the end plate secitons as required on more conventional structures. Similar plugging means may be employed for the opposite ends of the conduits, although this is not particularly useful since these opposite ends will be above water When the base is in place and may, therefore, consist of the conventional welded cap or closure plate which will be readily removable by more conventional means.

Accordingly, it is a primary object of the present invention to provide a floatable base of the general char acter described, having readily removable plugging means for sealing the drilling-through conduits against entrance of water while the structure is in floating condition.

A further object is the provision of a floatable base of the general character described, in which the plugging means employed for the several drilling-through conduits include releasable latch means for anchoring the plugging members in the respective conduits.

An additional object is the provision of an improvement in the method of operating a floatable base of the general character described.

Other and more specific objects and advantages of this invention will become more readily apparent from the following description when read in conjunction with the accompanying drawing which illustrates a useful embodiment in accordance with this invention.

In the drawing,

FIG. 1 is a perspective elevational view, with portions broken away, showing a floatable base of the multiple leg type, the base being shown in erect position;

FIG. 2 is a cross-sectional view through one of the leg elements taken along line 2-2 of FIG. 1;

FIGS. 3 and 4 are longitudinal, sectional views, both taken along lines 3-3 of FIG. 1, showing two positions of a plugging member in one of the drilling-through conduits;

FIG. 5 is a cross-sectional view taken along line 55 of FIG. 4;

FIG. 6 is a longitudinal, sectional view of a portion of one of the leg members illustrating, schematically, a ballasting system for the leg member; and

FIG. 7 is a view generally similar to FIGS. 3 and 4, illustrating an arrangement for withdrawing a plugging member from a drilling-through conduit.

Referring to the drawing, there is shown a floatable base comprising, in the illustrative embodiment, four large diameter cylindrical hollow legs, each designated generally by the numeral 11, interconnected by tubular cross bracing elements 12, 13 and 14 to form a rigid structure.

Each of the leg members 11 comprises outer and inner coaxial shells 15 and 16, respectively. The annular space between shells l5 and 16 is divided by radial dividers 17 angularly spaced to provide a plurality of compartments 18 through each of which extends a tubular drillingthrough conduit 19.

Inner cylinder I16 is compartmented by means of radial dividers 20 to form three additional compartments 21, each of which is similarly occupied by drilling-through conduit 19. The upper and lower ends of leg members 11 are sealed-01f about the several drilling-through conduits 119 by means of end plates 22 and 23, respectively (see FIG. 6). Lower plate 22 corresponds to a tube sheet in that it is provided with openings for receiving the related lower ends of the several drilling-through conduits, and is welded to the outer shell and about each of the drillingthrough conduits to form a water-tight seal for the lower end of the leg member. Upper end plate 23 may be of the same form, but since it will be readily accessible when the base member is in the vertical position, it may be a continuous plate welded across the upper end of the leg member and the enclosed conduits.

'Each of the drilling-through conduits is provided with a removable plugging member, designated generally by the numeral 25, for closing the lower end of the conduit, and will be described in detail hereinafter.

Conduits 26 and 27, fitted with valves 28 and 29, respectively, are arranged in each of the leg members by means of which 'water ballast may be admitted into the interior of the shells and 16, as well as the interiors of the several conduits 19, for purposes of up-ending and sinking the base when it has been transported to the drilling location. The ballasting arrangement is schematically illustrated since it will be obvious that any suitable and generally conventional system for destroying the buoyancy of the leg members may be employed in order to rotate the structure from the horizontal towing position to the vertical position, and for controllably sinking the up-ended base to rest on the underlying land. Should it become necessary or desirabe to move the base, the ballasting system may be employed for de-ballasting the legs and conduits, after the ends thereof have been closed off, to render the leg members buoyant for re-floating the base.

'Each of the plug members 25 includes a tubular latching body 30 dimensioned to slide freely through the bore of conduit 19 into a tubular housing 31, which may be an extension of conduit 19, and forms the lower end thereof when the structure is vertically disposed. The lower end portion 32 of latching body 30 is radially thickened and the bore thereof is closed at its outer (lower) end by means of a closure plate 33. The lower end of housing 31 is provided with an internal shoulder 34 against which the lower end of the plug member 25 will seat when the plug member has been fully inserted in housing 31, as seen in FIG. 4.

The wall of body 30, immediately above section 32, is provided with a plurality of radial windows 35, in each of which is mounted for radial movement a latching dog 36, the radial thickness of which is greater than the thickness of the wall of body '30.

The inner wall of housing 31 is provided with an annular groove 37 positioned to register with latching dogs 36 when the plugging member is seated against shoulder 34. In this position, dogs 36- may be moved radially outwardly into groove 37 for anchoring the plug member to the housing, in the manner to be hereinafter described.

A tubular expander mandrel 38 is mounted in the bore of body 30 for movement longitudinally thereof, and carries, intermediate the ends thereof, an outwardly projecting annular enlargement 39 adapted, when thrust behind dogs 36, to urge the latter radially outwardly. Dogs 36 are provided with bevelled front and rear edges 40 and 41, respectively, at their upper ends, and similarly bevelled front and rear edges 42 and 43, respectively, at their lower ends. Enlargement 39 has a bevelled lower end surface 44 for engagement with bevelled edge 41 of the latching dogs. The exterior of mandrel 38, above enlargement 39, is reduced in diameter to define an annular space 45 between the mandrel and the inner wall of latching body 30. An annular bushing 46 extends into annular space 45 and is provided with external threads 47 by means of which it is screwed into an internally threaded socket 48 provided at the upper end of body 30. The bore of bushing 46 is longitudinally slotted to form a splined connection to the upper portion of mandrel 38 by engagement with the splines 49 mounted on the mandrel whereby to permit relative longitudinal, but nonrotative, movement bet-ween mandrel 38 and body 30. A

plurality of coil springs 50 are mounted at angularly spaced points in the annular space in compression between a shoulder 51, defining the upper end of enlargement 39, and the inner end 52 of bushing 46. Guide rods 53 extend slidably through vertical openings 54 in the bushing through the center of springs into sockets 54a provided in enlargement 39.

Coil springs 50 bias mandrel 38 downwardly so as to urge enlargement 39 downwardly behind dogs 36 and thereby urge dogs 36 outwardly of windows 35. Initially, however, the mandrel is held in inactive relation to the dogs by means of shear pins 55 which connect body 30 to enlargement 39, as best seen in FIG. 3. The upper end of mandrel 38 carries a conventional fishing neck for attachment of conventional tools, such as an overshot, for pulling the plugging device out of conduit 19, and may also serve as a seat for engagement by a conventional spear when the latter is used for either inserting or withdrawing the plugging device.

Section 32 of the latching body is provided with a drain passage 56 which opens to the lower end of the plug body at one end and to the interior thereof between plate 33 and windows 35. Annular seals, such as O-rings 57-57, are mounted about the exterior of section 32 to seal with the wall of housing 31, and similar seals 5858 are mounted in the bore wall of section 32 on opposite sides of the inner end of passage 56, for purposes which will appear subsequently.

A plug member 25 may be inserted into a conduit 19 by sliding or pushing it from one end (the upper end) through the bore of the conduit until the lower end of section 32 seats on shoulder 34. With shear pins 55 in place, it will be seen that mandrel 38 will be in the position shown in FIG. 3, at which no outward thrust will be applied to dogs 36. Any suitable form of tool may be used to push the plug member home against seat 34. At this point, dogs 36 will be directly opposite groove 37, as seen in FIG. 4, whereupon, by a downward blow of sufficient force or application of sufficient weight against fishing neck 60, sufiicient downward force will be applied to mandrel 38 to break shear pins 55 and drive mandrel 38 down warly, forcing enlargement 39 over the bevelled surfaces 41 of the dogs and urging the latter outwardly into groove 37, thereby latching or anchoring the plug member to housing 31. Springs 50 will maintain this latching engagement of the mandrel with the dogs, as seen in FIG. 4. The lower end portion 38a of mandrel 38 will have moved downwardly behind section 32, so that the inner end of passage 56 will be sealed-off by engagement of seals 58-58 with the outer surface of mandrel 38, as seen in FIG. 4, thereby functioning as a sleeve valve closing the passage against entrance of water to the conduit.

When the structure is in place at a well location and it then becomes desirable to clear the bores of conduits 19, it is only necessary to run any sort of conventional fishing tool, such as a spear S (FIG. 7) or overshot, to grasp the upper end of mandrel 38 and apply an upward pull thereto sulficient to overcome the force of springs 50, whereupon the continued upward force will pull mandrel 38 upwardly in the bore of body 30 sufficiently to raise enlargement 39 above dogs 36 sufficiently to free the latter for movement inwardly in response to the reaction between bevelled edges 40 and the corresponding bevelled upper end surface of groove 37. Continued upward pull on mandrel 38 will thereupon be transmitted through bushing 46 to body 30, and thereby permit the entire plugging device to be pulled out of the bore of conduit 19. The initial upward movement of mandrel 38 releasing dogs 36 will raise end portion 38a above the inner end of passage 56 (FIG. 7, thereby opening the passage to permit drainage of water from the interior of conduit 19 above the plug member as the latter is drawn out of the conduit.

Although the fioatable base of the illustrative embodiment comprises a structure employing four leg elements arranged at the corners of a square, the invention herein disclosed contemplates other leg-type structures, including a so-called mono-pod embodying a single very large diameter leg or pedestal through which extend a plurality of drilling-through conduits and which will ordinarily be made buoyant for transporting to a marine location and then ballasted to place it vertically on location.

It will be evident that the plug members may be reinserted in the drilling-through conduits, should it become necessary or desirable to re-seal the lower ends of one or all of the conduits for any purpose, particularly if it should be desired to re-float the base structure.

It will be understood that various changes and modifications may be made in the details of the illustrative embodiment within the scope of the appended claims but without departing from the spirit of this invention.

What I claim and desire to secure by Letters Patent is:

1. A fioatable base for a marine drilling platform, comprising,

(a) elongate hollow leg means adapted to be floated to a marine drilling location for positioning in an upright platform-supporting position on a submerged land bottom,

(b) a plurality of longitudinally extending tubular drilling conduits enclosed within said leg means,

(c) means for closing the bore of said leg means about said conduits, 1

(d) plug means insertible into and removable through the upper ends of the bores of said conduits for closing the ends of said conduits which will be disposed adjacent said land bottom when the leg means attain said upright position, said plug means including:

'(i) a tubular body having a closed lower end,

(ii) annular seal means disposed about the body for sealing engagement with the bore wall of the related conduit, and

(iii) radially movable latch means engageable with shoulder means on the related conduit adjacent the submerged end thereof for releasably securing said plug means thereto.

2. A fioatable base according to claim 1, wherein said hollow leg means comprises a plurality of spaced apart tubular legs and interconnecting cross-bracing elements.

3. A fioatable base according to claim 1 including means for introducing ballast into said leg means to attain said upright position.

4. A fioatable base according to claim 1, wherein said latch means comprises:

(a) latching dogs carried by said body for movement into and out of latching engagement with said shoulder means carried by said conduit, and

(b) a latching mandrel mounted on said body for movement between a first position holding said dogs in latching engagement with said shoulder means and a second position releasing said dogs from said shoulder means whereby to permit withdrawal of said plug means from said conduit.

5. In a fioatable base according to claim 4, resilient means biasing said mandrel toward said first position.

6. In a fioatable base according to claim 4, frangible means initially securing said mandrel to said body in said second position and releasable by end-wise force applied to said mandrel.

7. In the method of constructing a drilling platform at a marine location, wherein a platform base comprising a hollow leg means enclosing a plurality of drilling-t'hrough conduits is made buoyant for floating the same to the marine location and thereat submerged to rest in vertical position on a submerged land bottom,

the improvement which comprises, inserting into the bores of said conduits adjacent the ends thereof which will be adjacent said land bottom removable sealing plug means whereby to seal said conduits during fioatation of the base, and after the base is in vertical position on the land bottom withdrawing said plug means upwardly through said conduit bores to clear the same for drilling through operations.

8. In a method according to claim 7, the further improvement which comprises re-inserting the plug means in the bores of said conduits to seal the same, to enable restoring the buoyancy of said base for refloating the same.

References Cited UNITED STATES PATENTS 2,775,869 l/ 1957 Pointer 61-46.5 2,857,744 10/1958 Swiger 6146.5 3,130,788 4/1964 Cochran et al. 166-217 3,209,544 10/1965 Borrmann 61--46.5 3,305,021 2/1967 Lebourg 166-122 JACOB SHAPIRO, Primary Examiner.

U.S. C1. XJR. 166-135, 217 

